diff --git a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/NetworkGraphDatastore.java b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/NetworkGraphDatastore.java
new file mode 100644
index 0000000..288b1f4
--- /dev/null
+++ b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/NetworkGraphDatastore.java
@@ -0,0 +1,277 @@
+package net.onrc.onos.ofcontroller.networkgraph;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import net.onrc.onos.datastore.RCObject;
+import net.onrc.onos.datastore.RCObject.WriteOp;
+import net.onrc.onos.datastore.topology.RCLink;
+import net.onrc.onos.datastore.topology.RCPort;
+import net.onrc.onos.datastore.topology.RCSwitch;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import edu.stanford.ramcloud.JRamCloud.ObjectDoesntExistException;
+import edu.stanford.ramcloud.JRamCloud.ObjectExistsException;
+import edu.stanford.ramcloud.JRamCloud.WrongVersionException;
+
+/**
+ * The southbound interface to the network graph which allows clients to
+ * mutate the graph. This class will maintain the invariants of the network
+ * graph. The southbound discovery modules will use this interface to update
+ * the network graph as they learn about the state of the network.
+ *
+ * Modification to the Network Map by this module will:
+ * 1. Writes to Cluster-wide DataStore.
+ * 2. Update ONOS instance In-memory Network Map.
+ * 3. Send-out Notification. (TBD)
+ *    (XXX: To update other instances In-memory Network Map,
+ *          notification should be triggered here.
+ *          But if we want to aggregate notification to minimize notification,
+ *          It might be better for the caller to trigger notification.)
+ *
+ */
+public class NetworkGraphDatastore {
+	private static final Logger log = LoggerFactory.getLogger(NetworkGraphDatastore.class);
+
+	private static final int NUM_RETRIES = 10;
+	
+	private final NetworkGraphImpl graph;
+
+	public NetworkGraphDatastore(NetworkGraphImpl graph) {
+		this.graph = graph;
+	}
+
+	public void addSwitch(Switch sw) {
+		log.debug("Adding switch {}", sw);
+		ArrayList<WriteOp> groupOp = new ArrayList<>();
+
+		RCSwitch rcSwitch = new RCSwitch(sw.getDpid());
+		rcSwitch.setStatus(RCSwitch.STATUS.ACTIVE);
+
+		// XXX Is ForceCreating Switch on DB OK here?
+		// If ForceCreating, who ever is calling this method needs
+		// to assure that DPID is unique cluster-wide, etc.
+		groupOp.add(WriteOp.ForceCreate(rcSwitch));
+
+		for (Port port : sw.getPorts()) {
+			RCPort rcPort = new RCPort(sw.getDpid(), (long)port.getNumber());
+			rcPort.setStatus(RCPort.STATUS.ACTIVE);
+			rcSwitch.addPortId(rcPort.getId());
+
+			groupOp.add(WriteOp.ForceCreate(rcPort));
+		}
+
+		boolean failed = RCObject.multiWrite( groupOp );
+
+		if ( failed ) {
+		    log.error("Adding Switch {} and its ports failed.", sw.getDpid());
+		    for ( WriteOp op : groupOp ) {
+			log.debug("Operation:{} for {} - Result:{}", op.getOp(), op.getObject(), op.getStatus() );
+
+			// If we changed the operation from ForceCreate to
+			// Conditional operation (Create/Update) then we should retry here.
+		    }
+		}
+		else {
+			// Publish event to the in-memory cache
+			graph.addSwitch(sw);
+		}
+
+	}
+
+	public void deactivateSwitch(Switch sw) {
+		log.debug("Deactivating switch {}", sw);
+		RCSwitch rcSwitch = new RCSwitch(sw.getDpid());
+
+		List<RCObject> objectsToDeactive = new ArrayList<RCObject>();
+
+		for (int i = 0; i < NUM_RETRIES; i++) {
+			try {
+				rcSwitch.read();
+				rcSwitch.setStatus(RCSwitch.STATUS.INACTIVE);
+				objectsToDeactive.add(rcSwitch);
+
+				for (Port p : sw.getPorts()) {
+					RCPort rcPort = new RCPort(sw.getDpid(), (long)p.getNumber());
+					rcPort.read();
+					rcPort.setStatus(RCPort.STATUS.INACTIVE);
+					objectsToDeactive.add(rcPort);
+				}
+			} catch (ObjectDoesntExistException e) {
+				log.warn("Trying to deactivate an object that doesn't exist", e);
+				// We don't care to much if the object wasn't there, it's
+				// being deactivated anyway
+			}
+
+			try {
+				for (RCObject rcObject : objectsToDeactive) {
+					rcObject.update();
+				}
+				break;
+			} catch (ObjectDoesntExistException e) {
+				// Unlikely, and we don't care anyway.
+				// TODO But, this will cause everything else to fail
+				log.warn("Trying to deactivate object that doesn't exist", e);
+			} catch (WrongVersionException e) {
+				// Need to re-read and retry
+			}
+		}
+	}
+
+	public void addPort(Switch sw, Port port) {
+		log.debug("Adding port {}", port);
+		RCSwitch rcSwitch = new RCSwitch(sw.getDpid());
+
+		try {
+			rcSwitch.read();
+		} catch (ObjectDoesntExistException e) {
+			log.warn("Add port failed because switch {} doesn't exist", sw.getDpid(), e);
+			return;
+		}
+
+		RCPort rcPort = new RCPort(port.getSwitch().getDpid(), (long)port.getNumber());
+		rcPort.setStatus(RCPort.STATUS.ACTIVE);
+		// TODO add description into RCPort
+		//rcPort.setDescription(port.getDescription());
+		rcSwitch.addPortId(rcPort.getId());
+
+		writeObject(rcPort);
+		writeObject(rcSwitch);
+	}
+
+	public void deactivatePort(Port port) {
+		log.debug("Deactivating port {}", port);
+		RCPort rcPort = new RCPort(port.getSwitch().getDpid(), (long)port.getNumber());
+
+		for (int i = 0; i < NUM_RETRIES; i++) {
+			try {
+				rcPort.read();
+			} catch (ObjectDoesntExistException e) {
+				// oh well, we were deactivating anyway
+				log.warn("Trying to deactivate a port that doesn't exist: {}", port);
+				return;
+			}
+
+			rcPort.setStatus(RCPort.STATUS.INACTIVE);
+
+			try {
+				rcPort.update();
+				break;
+			} catch (ObjectDoesntExistException | WrongVersionException e) {
+				// retry
+			}
+		}
+	}
+
+	public void addLink(Link link) {
+		log.debug("Adding link {}", link);
+		RCLink rcLink = new RCLink(link.getSourceSwitchDpid(), (long)link.getSourcePortNumber(),
+				link.getDestinationSwitchDpid(), (long)link.getDestinationPortNumber());
+
+		RCPort rcSrcPort = new RCPort(link.getSourceSwitchDpid(), (long)link.getSourcePortNumber());
+		RCPort rcDstPort = new RCPort(link.getDestinationSwitchDpid(), (long)link.getDestinationPortNumber());
+
+		for (int i = 0; i < NUM_RETRIES; i++) {
+			try {
+				rcSrcPort.read();
+				rcDstPort.read();
+				rcLink.create();
+			} catch (ObjectDoesntExistException e) {
+				// port doesn't exist
+				log.error("Add link failed {}", link, e);
+				return;
+			} catch (ObjectExistsException e) {
+				log.debug("Link already exists {}", link);
+				return;
+			}
+
+			rcSrcPort.addLinkId(rcLink.getId());
+			rcDstPort.addLinkId(rcLink.getId());
+
+			rcLink.setStatus(RCLink.STATUS.ACTIVE);
+
+			try {
+				rcLink.update();
+				rcSrcPort.update();
+				rcDstPort.update();
+				break;
+			} catch (ObjectDoesntExistException | WrongVersionException e) {
+				log.debug(" ", e);
+				// retry
+			}
+		}
+		
+		// Publish event to in-memory cache
+		graph.addLink(link);
+	}
+
+	public void removeLink(Link link) {
+		log.debug("Removing link {}", link);
+		RCLink rcLink = new RCLink(link.getSourceSwitchDpid(), (long)link.getSourcePortNumber(),
+				link.getDestinationSwitchDpid(), (long)link.getDestinationPortNumber());
+
+		RCPort rcSrcPort = new RCPort(link.getSourceSwitchDpid(), (long)link.getSourcePortNumber());
+		RCPort rcDstPort = new RCPort(link.getDestinationSwitchDpid(), (long)link.getDestinationPortNumber());
+
+		for (int i = 0; i < NUM_RETRIES; i++) {
+			try {
+				rcSrcPort.read();
+				rcDstPort.read();
+				rcLink.read();
+			} catch (ObjectDoesntExistException e) {
+				log.error("Remove link failed {}", link, e);
+				return;
+			}
+
+			rcSrcPort.removeLinkId(rcLink.getId());
+			rcDstPort.removeLinkId(rcLink.getId());
+
+			try {
+				rcSrcPort.update();
+				rcDstPort.update();
+				rcLink.delete();
+			} catch (ObjectDoesntExistException e) {
+				log.error("Remove link failed {}", link, e);
+				return;
+			} catch (WrongVersionException e) {
+				// retry
+			}
+		}
+	}
+
+	public void updateDevice(Device device) {
+		// TODO implement
+	}
+
+	public void removeDevice(Device device) {
+		// TODO implement
+	}
+
+	// TODO what happens if this fails? why could it fail?
+	private void writeObject(RCObject object) {
+		for (int i = 0; i < NUM_RETRIES; i++) {
+			try {
+				object.create();
+			} catch (ObjectExistsException e) {
+				try {
+					object.read();
+				} catch (ObjectDoesntExistException e1) {
+					// TODO Auto-generated catch block
+					log.error(" ", e);
+					return;
+				}
+			}
+
+			try {
+				// TODO check API for writing without caring what's there
+				object.update();
+				break;
+			} catch (ObjectDoesntExistException | WrongVersionException e) {
+				log.debug(" ", e);
+				// re-read and retry
+			}
+		}
+	}
+}